Automatic torque compensator



July 7, 1953 H. T. JENSEN I 2,644,534

AUTOMATIC TORQUE COMPENSATDR Filed Oct. 5, 1946 v 5 Sheets-Sheet l H. T.JENSEN INVENTOR ATTORNEY July 7, 1953* H. T. JENSEN 2,

AUTOMATIC TORQUE COMPENSATOR FiledOct. 5, 1946-, r 5 Sheets-Sheet 2 H.TJJENS'EN mvem'oa ATTORNEY July 7, 1953 1'. JENSEN 4,

AUTOMATIC TQRQUE 'COMPENSIATOR Filed Oct. 5, 1946 I 5 Sheets-Sheet 5 IPITCH CONTROL LINYK- NOR MAL RANGE POWER o- P|TOH CONTROL ARM-8| BLADECHORD I NORMAL r 757 W .I34 A j NORMAL RANGE POWER on H. T. JENSENINVENTOR ATTORNEY July 7, 1953 H. 'r. JENSEN AUTOMATIC TORQUECOMPENSATOR Filed Oct. 5, 1946 5 Sheets-Sheet 5 INVENTOR Mflm H. T.JENSEN ATTORNEY Patented July 7, 1953 2,644,534 AUTOMATIC TORQUECOMPENSATOR Harry '1. Jensen, Milford, Conn., assignor to United.Aircraft Corporation, East Hartford, Conn, a corporation of DelawareApplication October 5, 1946, Serial No. 701,605

4 Claims.

This invention relates generally to rotary wing aircraft; moreparticularly to craft of the helicopter type; and more specifically toimproved structure for compensating the torque of rotors of helicopters,to improved automatically operated structure for controlling the thrustof torque compensating rotors, and to improved means for obtaining andmaintaining pitch trim in helicopters.

In presently known helicopters of the type employing an auxiliary rotoraft of the main rotor for compensating the torque of the latter, thepilot must attend constantly to the counterbalance of main rotor torqueby adjusting the thrust of the torque compensating rotor, sometimescalled the tail rotor. Such action on the part of the pilot may be doneonly by neglecting other controls at times, and may not be doneaccurately at all by an unskilled pilot thereby causing erraticoperation of the helicopter and Waste of fuel.

Heretofore, proposals have been made to provide gyroscopes, or the like,to maintain a given heading for a craft by actuation of a torquecompensating rotor. Such devices, while probably satisfactory to adegree in forward flight, are nevertheless subject to a time delayaction, or lag, because of the fact that an undesirable heading must beattained before any corrective force whatever is brought into play. Whenbrought into play, the condition is usually Worsening so that an excessof force 'must be used to overcome the condition and to return thehelicopter to the desired heading, which action may cause hunting, andis quite likely to waste fuel.

Hence, an object of this invention is to provide improved automaticmeans for counteracting the torque of the sustaining rotor assubstantially an instantaneous action or function responsive to torqueof the sustaining rotor.

Another object is to provide an improved torque compensating device forhelicopters, or the like.

A feature is to provide improved structure for obtaining automatictorque compensation while retaining a predetermined component of lift inthe structure.

Still further objects and features reside in the mechanical, electrical,and hydraulic details of construction and combinations of parts and willbe either obvious or pointed out in the following specification andclaims.

In the drawings,

Fig. l is a side elevational view of a helicopter including my inventionand showing parts thereof diagrammatically;

component compensating linkage superposed on a chart showing theoperation thereof;

Fig. 6 is a chart of component compensation requirements Fig. 7 is achart of the blade pitch change to effect component compensation;

Fig. 8 is a diagrammatic view of an electrical automatic torquecompensation control system;

Fig. 9 is a wiring diagram of the structure shown in Fig.8; j

.Fig. 10 is a diagrammatic view of a hydraulic modification of theinvention; r

Fig. 11 is a diagrammatic view of a hydromech'anical modification; and

Fig. 12 is a diagrammatic view of a hydraulic drive without theautomatic torque compensation feature.

Referring more in detail to the drawings, and first to Fig. l, ahelicopter body [8 supports a suitable engine for turning sustainingrotor blades 22 through a shaft-24. A reduction gear 26, which may be oftheplanetary gear type, is connected between the engine 20 and the shaft24. A torque compensating rotor drive shaft 28 may also be driven by theengine 25 or through the reduction gearing 26 as best suits theinstallation, and the shaft 28 turns torque compensating rotor blades 30shown as mounted upon a rotatable empennage or tail piece 32 carried atthe rearmost extremity of the body 18. In the modification illustratedin Fig. l, the rotor blades 30 of the torque compensating rotor arerotated in and out of the plane of the paper by a control rod 34 whichrotates the tail piece 32. The control means for rotating thecompensating rotor 30 comprises an automatic control device 35responsive to torque of the sustaining rotor blades 22 through the gearbox 26, which automatic control 35 works in conjunction with and may beover-ridden by manual control pedals or stick 36, or the like.

In Fig. 2, the automatic shown diagrammatically, but in more detail. Thegear box 26 may be mounted upon the drive shaft 24 on bearings so thatit can rotate relative to either the input or output ends of the controldevice 35 is" 3 drive shaft. Thus, as power is supplied from the engine20 through the gear box 26 to the drive shaft 24 and thence to the rotorblades 22, there will be a counter-torque force tending to causerotation of the gear box 26 if it were not secured. In this invention, Iprefer to connect the gear box 26 to the helicopter body l8 by an arm 37and a resilient connection shown as a spring 38. To prevent vibrationand hunting action of the control device 35, a dash pot 463 is pivotallymounted by a yoke 42 to the body I8 and contains a piston M connected bya rod it to the arm 31. With such construction, as the torque to thedrive shaft 24 changes, the gear box 26 will tend to rotate in onedirection or the other to change the tension of the spring 38. Suchmovement will cause movement to the right or left, as the case may be,of a push pull rod 50, which motion will cause tilting of the compensating rotor 36 in a manner to be described more fully hereinafter.

The manual control portion of this automatic torque compensatingmechanism is operated from the control stick 36 (Fig. 1) which moves apush pull rod 52 to rock a bell crank A having its mid-pivot connectedwith the body [8 of the helicopter. Fore and aft movement of the pushpull rod 52 will cause rotation of the bell crank 5d, and verticalmovement of a push pull rod 56 connected with the mid-pivot of togglearms 58 which upon being moved at their mid point will move a rod 60towards or away from the rod 59. Movement of the rod 69 under theinfluence of the automatic control means 35 in response to main rotortorque or in response to movement of the control stick 36 will causemovement of the torque compensating rotor blades 36 in a manner now tobe described.

The rod 56 connects with a bell crank 62 which changes direction ofmotion for the rod 59 to right angles with a rod 64. That is, the pushpull direction of rod 66, which is fore and aft in the helicopter, ischanged 90 by bell crank 52 so that rod 6d reciprocates in a directiontransverse to the fore and aft axis of the helicopter. This is necessarywith rod connections because the torque compensating rotor 30 movesaround in a plane at an angle to the direction of motion of the rods 50and 65. Movement of the rod 64 will move a rack 66, confined in guiderolls 58,

back and forth. The rack 66 engages a toothed segment-m'that isconnected with'a torque compensating rotor cone l2 so that both the coneall) tion. Hence, the manual means 36 may be used to trim the craft atall times, and the automatic control device 35 will superpose itsfunction upon the function of the manual means 35 so that the pilot Willbe relieved of a large percentage of the duty of attending to the torquecompensation function of the tail rotor blades 33 and may give hisattention to trimming the craft for heading and for variations in load.For steady flight the control stick 35 may be locked in position and thecontrol means 35 will adjust automatically for torque changes duringflight.

Referring again to Fig. 2 and also to Figs. 3 and 4, the pitch of theblades 36 is controlled through a push pull rod 89 connected by a pivot82 at its lowermost end to a crank 8 The rod Bil is ,journalled forsliding motion within the cone l2 and hence rotates with the cone. Thecrank 84 is pivoted upon pins 86 at points out of registry with a linecontaining the pivots is for the arcuate segment ill and the tail conel2. Thus,'as the tail cone I2 is rotated about the pivot '16, the pushpull rod 8t will be reciprocated within the cone ina manner to bedescribed more fully, below. Reciprocation of the rod 8i! causesmovement up and down of a link 38 (Fig. 2)

mounted at the uppermost extremity of the rod 38 and connected by apivot 9G to the blade 30. The blade is mounted upon a pivot at its hubso that its pitch can be changed. This structure is conventional invariable pitch propellers and rotor blades and hence has not beendisclosed in detail. Accordingly, motion of the rod iltvvill causechange in pitch and hence change in thrust for a given rotational speedof the rotor blades 30.

While many of the details of construction of the tail rotor mechanismmay differ in design and arrangement'from that of this disclosure, thosedetails will be described to facilitate the reproduction and practice ofmy-invention, Referring to Figs. 3 and 4, the rotatable tail piece 32includes a streamline fairing 92 and has a sealoff skirt S4 slidablewithin the fairing and connected to the cone 12. A base member 9% may besecured to the helicopter body It and support all of this structure. Thedrive shaft 28 turns a bevel pinion 91 which rotates a bevel gear 98splined to -a tail rotor drive shaft lot which may and the segmentrotate about a pivot is (Fig. 3).

Hence, movement of the rod 68 will cause movement to the right or leftin an arcuate path of the rotor blades 36 so that the lateral componentof thrust of the rotor blades can be altered to accommodate the variablerequirements of torque of the main rotor blades 22. As pointed outabove, this motion can be obtained either by motion of the gear box 26which moves the rods .59 and 60 together as the rod 56 pivots around itspoint of connection with the bell crank 54; or can be obtained bymovement of the rod 52 by the manual control stick which lengthens orshortens the toggle 58 with respect to they points of connection of therods and 68 with the automatic control device 35. Accordingly, it isseen that the automatic control device v35 uses the position of themanual control means 35 as a reference in performing its controlfunction, and the manual means 36 also makes use of the position of theautomaticcontrol means 35 as a reference in performing its controlfuncbe suitably connected to a hub, not shown, for the tail rotor blades30. The cone 12 may be mounted in bearings lli? to facilitate rotationthereof. Movement of. the cone 52 may be opposed by a centering springI94 that connects between a fixed bracket Hit and an arm Q68 secured tothe cone 12. A damper H6 which may be similar to the damper it (Fig. 2)may also be supplied to prevent hunting and vibration of the cone 12 andthe rotor blades 36 connected therewith. The pinion 9'! may rotate in adirection with respect to the torque requirementfof this device so thatthe spring are may act at a predetermined spring rate to permit tiltingof the cone T2 in a direction to compensate for torque of the mainrotor. Also, this direction of rotation may be such that the torquerequire ments of the tail rotor in part compensate the torquerequirements of the main rotor;-for example, the two rotors may rotatein opposite directions but at different speeds. 3

Referring now to Fig. 5, a linkage is shown for causing the shaft 88 tomove upwardly with respect to the cone 12 and follow substantially apath H2 with respect to a path H4. The path H4 may be the path of animaginary point connected with the cone 12, and the path H2 is the pathof the pivot 82 of the crank 84; Theorem 64 may contain a knee joint II6 including a pivot H8 and a spring I20 biasing arms I22 and I24 of thecrank 86 into engagement with stop shoulders I26. A stop I28 may beengaged by the arm I22 after a predetermined rotation in a clockwisedirection of the crank 86 so that the knee joint H6 will yield as shownin dotted lines at the left of the figure.

Referring now to Fig. 6, that portion of the operation of the devicediagrammatically shown in Fig. is repeated at the'lower-left hand side,and torque requirements to maintain a substantially constant lift areshown diagrammatically at I30. It will be understood that while thechart is drafted upon linear coordinates, that the nonlinearrequirements of change of lift for a change in incidence of an airfoilshould also be included in the calculationof requirements, andmechanical advantages of the several linkages should also be compensatedwith the spring tension available in the springs 38, and I04, Figs. 2and 4, or other springs and dampers as used to obtain a correct resultincluding friction losses and the like; and that the disclosure isillustrative only and not restrictive. Accordingly, the chart I80 merelyshows the function of thecrank 86 to maintain substantially a constantlift represented by a line I32 by changing incidence of the blades 30.The motion of the lower end of the rod 80 represented by 'a radiallyextendingline I84 is on a two-toone mechanical advantage basis withrespect to the line I32. In other words, the lower points move one-halfthe distance of the upper points in the chart of Fig. 6, and such motioncan be obtained by mechanical linkages as required. The lines I I2 andH4 have been repeated in Fig. 6 and represent the change required at H2with respect to a given reference line I I 4 which would trace a pointof rotation around the pivot point 14 for the cone 12. The crank 84rotates around pivots 86 by action of the rod 60 to obtain the path oftravel II2 of pivot 82 to cause the pitch of the blades 30 to follow theline I32 rather than a line I 36 which is used as a base to indicatepitch change action without the pitch compensating crank 84.

Fig. 7 diagrammatically represents the normal range of pitch change forpower on conditions at the tail rotor and the motion of the uppermostend of the pitch control rod 80 at I40. Motion as at I40 will cause apath of travel I42 for the point of connection of the link 88 with theblades 30. The point I42 will travel an arcuate path whereas the pointI40 will travel a linear path and hence a correction may be required indesign of the pivot point 86 for the crank 80 to compensate for theabberation between linear motion and rotative motion. Of course it isunderstood that the path I46 can be arranged with respect to the pathI42 so that this error is of very low order and probably negligible.

Figs. 8 and 9 show an electrical device for performing substantially thesame function as the mechanical device described above as regardsautomatic torque compensation of the main sustaining rotor by the actionin response to main rotor torque of an automatic control mechanismacting upon the tail rotor. Referring first to Fig. 8, the engine 20rotates the blades 22 through the drive shaft 24 and gearing containedin the housing 26. The tail rotor drive shaft 28 turns the tail rotorblades 30 through suitable gearing I50. The pitch of the blades 30 ischanged by means of a worm and pulley I52 substantially in the pedalsI58 will move the cables I56 differentially to rotate the pitch changingmechanism I52 to change the pitch of the blades and hence the thrust ofthe blades for a given speed of rotation thereof. The automatic controlmechanism 65 may include\a spring and damper of structure identical tothat disclosed in Fig. 2. The arm 31 may carry a potentiometer wiper Iwhich movesover a potentiometer I62 tochange the balance in a bridgecircuit I64 in a manner now to be described.

The potentiometer I62 controls the action of a double relay I63 to movea contact arm I66 into engagement selectively with contacts I68 and I10.Relay coils I12 and I14 may be selectively energized by separate legs ofthe bridge circuit.

A battery or generator I16 or the like supplies current to the relaycoils I12 and I14 through the following circuits. Energyfor the coil I12may come from the'battery I16 through a wire I16, the wiper I60, thelower half of potentiometer I62, wire I80, the coil I12, wire I82, thelower half of a potentiometer I84, a wiper I86 positioned by the motorI54 and wire I68 back to the other side of the battery I16. Current forthe relay coil I14 is supplied from the battery I16 through the wireI18, wiper I60, the upper part of the potentiometer I62, wire I90, athree-way switch I82, wire I84, a trim adjusting potentiometer I96, wireI98, coil I14, wire 200, the upper portion of potentiometer I84, motordriven wiper 86, and wire I88 back to the battery I16. Energization ofeither of the coils I12 and I14 will cause movement of the relaycontacts I66 into engagement with either the contact I68 or I10. Ifdesired, the relay contact I66 may be suitably clamped and magneticallyor spring centered to have a neutral position as shown to preventconstant action in one direction or the other of the control device.However, such constant action may be desirable in some craft andthecentering mechanism may be eliminated to increase the sensitivity of theautomatic control system. The contacts I68 and I10 selectively controlenergization of field windings 202 and 204 for the motor !54. Energy forthese windings is fed from the battery I16 through the wire I16 to acommon wire 206 through the motor armature to either motor I54 willrotate in a first direction to turn a worm 2I2 and thus a gear 2E4 tochange the pitch of the blades 30. When the coil 204 is energized, theworm 2I2 will rotate in the opposite direction to change the pitch ofthe blades 30 in the opposite sense.

When more torque is required by the sustaining rotor blades 22, and theyare turned clockwise, the gear box 26 will be biased in a direction torotate the same counter-clockwise and compress the spring 38. This willcause the wiper 7 I60 to in'ove upwardlybn the potentiometer I62. Atthis time, current from the battery I76 through the wires I78 and thewiper I66 will have less resistance through-the wires I96, the switchI92, the wire I94, a trim adjustment I56, the relay coil I74, the wire260, the upper part of potentiometer I 84, the motor wiper I 86 and thewire I88 back to the battery thanit will have through that circuit whichenergizes the coil I72 and which was traced above. Accordingly, thecontact arm of the relay I64 will be drawn into engagement with thecontact I76 which will energize the field winding 202 of the motor I54to rotate thecontrol mechanism I52 in a direction to change the pitch ofthe blades 36 of the tail rotor in a direction to counterbalance suchtorque so that the body of the helicopter will not be rotated in adirection opposite to the direction of rotation of the main sustainingrotor blades 22. Movement of the motor I54 will cause the potentiometerwiper I86 to move downward in a direction to increase the resistance inthe above named circuit to the relay coil. I74 and to decrease theresistance in the circuit to the relay coil I72 till such time that theenergization of each is substantially equal, at which time the relaycontact I66 will move into the mid-position shown if a centering deviceis used therewith, or into engagement with the contact I68. It is to beunderstood that if desired, known anticipating circuits canbe employedin connection with the bridge circuit described above to preventovershooting or hunting of the control arrangement described above. Upona decrease in torque requirements in the main rotor the po= tentiometerwiper I60 moves downwardly to energize the relay coil I72 so that themotor 554 is operated to change the pitch in the opposite sense thandescribed immediately above to balance the requirements of the system toprevent rotation of the body of the helicopter in the direction ofrotation of the main rotor blades 22.

It is possible in the electrical control system to use the automaticportion thereof as a power booster for the manual control system. Inother words, the pedals I58 can move the cables I56 to change pitch ofthe blades 36 at all times, but by also employing a potentiometer 226with a wiper 222 connected to at least one of the pedals I58, thecontrol system described above can be operated in a manner to unbalancethe bridge under the influence of manual control so that the motor I52can aid the pilot in his manual operation to prevent fatigue or toreduce the manual force required to operate the controls of a largehelicopter. To obtain such aided manual control, the switch I92 may bemoved into engagement with a contact 224. At this time the current tothe coil I74 will be variable upon he operation of the pedal I58, andthe coil I72 of the bridge circuit will act as a reference. Hence, thepilot may move the pedal I58 to include more or less than a givenresistance to raise or lower the potential of the coil I74 with respectto the now reference coil I72 to cause the motor I52 to operate in onedirection or the rotor to maintain a, given heading, plus enough reservepower for control purposes. However, when the helicopter .is in forwardflight, up to a certain point there is a weathercock action of theempennage section and it is conventional practice to design suchsections to obtain the best efiiciency in forward flight when fiying'ina somewhat crabwise manner so that a maximum amount of torque isavailable to the sustaining and propelling rotors and only a minimum oftorque is required in the torque compensating and controlling tailrotor. In order to obtain the maximum in efficiency in a helicopter ofthis type, I propose to introduce means responsive to speed of thehelicopter, at least in the forward sense, for compensating the actionof the automatic torque compensating built in structure described above,to provide for automatic reduction in torque requirement during forwardspeed. A Pitot head 230 may lead to a suitable statically balancedbellows or diaphragm or the like 232 which may position a potentiometer234 shown by way of example. It is to be understood that capacitance orinductance types of sensitive elements could also be used, and that theymay require less operating force, or that suitably boosted electroniccircuits could be incorporated in any known manner. As shown in thisfigure, movement of the bellows 232 in response to velocity changes atthe Pitot head 230 will cause movement of the potentiometer wiper 234 tochange the resistance of a potentiometer 236. The switch I92 may berotated into engagement with a contact 236 so that he'change inpotential or resistance by reason of motion of the wiper 234 will causea change in energization of the relay coil I74 against the energizationof relay coil I72 which again will serve as a reference in a mannersimilar :to that described above in connection with augmentation incontrol by the power boost action for the manual controls. It is to beunderstood that it would be possible to place themanual control and thespeed compensator in series if desired, by means of a second switch, notshown, to obtain both the manual power boost function and the speedcompensation function simultaneously.

7 Referring now to the hydraulic modification shown in Fig. 10, theengine 20 turns the sustaining rotor blades 22 by means of a shaft 24driven from the engine 20 through the gear box 26. The tail rotor blades36 are driven hydraulically from the engine 26'which drives a shaft 240that rotates a pump 242 that in turn supplies liquid to a hydraulicmotor 244 through a high pressure pipe 246. The high pressure pipe 246contains an accumulator 248 to reduce surging. Low pressure fluid fromthe motor 244 flows into a return pipe 256 connected to a sump 252,which sump connects with a supply pipe 254 equipped with a strainer 2 56and a dirt pocket 253 to the pump 242. The-pump 242 may be of thevariable capacity type, such as those pumps in which pistons are changedin displacement by shifting the barrel containing the cylinders andpistons, and may be changed in its displacement by a hydraulic strokemotor 266 which operates upon an arm 262 for changing the capacity ofthe pump 242. The stroke motor 266 may be biased downwardly by a spring264 which may conveniently return the arm 262 to a position in which thepump 242 has the highest torque capacity with respect to the motor 244.The stroke motor 260 is connected hydraulically by a, pipe 266 with'amanually operated stroke motor 268 and to an automatically operatedstroke motor 210.

The manually operated stroke motor 268 is connected with the foot.pedals 212 by linkage 214 and may conveniently be spring biased as by aspring 216 so that the operator of the pedals 212 will not need to exerta large force through a distance to operate the stroke motor 269.Operation of the pedals 212 will move the stroke motor 268 to positionthe stroke motor 260' and thus the arm 262 to change th capacity of thepump 242 with respect to the motor 244. and change the speed of rotationof the blades 30 to change the thrust thereof and thus control theattitude of the helicopter.

The automatically operated stroke motor 276 is biased by a spring 218 ina direction'to maintain the oil in pipe 266 at a low pressure and thepressure within a chamber 280 at a relatively high pressure. The chamber289 is variable in volume by a piston 282 which is moved towards theleft in response to an increase in torque of the main rotor blades 22.The spring 218 affords a resilient return and can be operative'upon apiston within the stroke motor 279 of' a size in proportion to thepiston 262 to maintain the pressure in the pip 266 at the'desired valueand the pressure in the chamber 280 at a predetermined higher value tocounteract the main rotor torque. Motion of the piston 282 will causethe stroke motor 210 to actuat the stroke motor 269 to move the arm 262of the pump 242 in a direction to speed up the rotation of the motor 224and thus change the thrust exerted by the blades 36 which, in thismodification, may be of fixed pitch, if desired, or may be made with avariable pitch for trimming purposes, if desired, in a,

manner to be described in connection with Fig. 12.

Referring now to Fig. 11, a mechanical hydraulic system is shown, andthe drive from the engine 20 to the blades 22 may be substantially thesame as set forth in connection with the figures described above. Inthis modification, however, a substantially constant speed and capacitypump 290 is connected with a constant displacement motor 292. Thi typeof pump and motor combination is usually simpler to manufacture andhence more economical to install.

To provide for variation in the thrust of the blades 30, I provide aby-pass valve 294 which is controlled by cables 296. As the valve 294 ismoved in one direction or the other, more or less high pressure fluid isfed from the pump 299 to the motor 292 or to the sump. A modifiedmechanical structur i also provided at 306for causing an automaticcontrol mechanism 302 responsive to torque of the gear box 26 tolengthen and shorten one or the other of cables 296 depending upon thecounter-torque force exerted by the gear box 26, which structure 992 incombination with the cables 296 and the mechanical adjustment mechanism390 work with the manual pedals 394 as a reference. For manual controlpurposes, the pedals 394 may be depressed differentially and as thelower cable 296 moves in one direction, the upper cable 296 can move inthe opposite direction, and a link 366 connecting the mid-points oftoggles 398 and 3m will rotate. Spring connections may be provided inthe cables 296 as required, to take up any slack which might exist uponexcess movement of the cables 296. The toggle device 309 is uided insuitable rolls 3|2.

The automatic torque responsive mechanism action willobtain, and

stantially the same 302 comprises toggle arms 314 spring biased up wardas by a spring '3l6 which acts upon a dash pot 3l8 that will dampen anyvibrations occurring in the gear box 26. As the torque from the gear.box 26 increases, the toggle arms 3| 4 are rotated so that their'commonconnection point is urged downwardly, which pushes a shaft 320downwardly to strai'hten out the upper toggle 388 more and move theuppercabl 296 towards the right, and bend the lower toggle Sill-more to move'the lower cable 296 towards the left. This will raise the armof thevalve 294 so that less fluid will feed from the high pressure line fromthe pump 299 back to the sump and more high pressure fluid will be fedto the motor 292 whereby the power input to and hence the thrust of theblades 96 Will be increased. Upon a decrease in torque in the gear box26, the opposite the thrust of the blades 30 will be decreased.

Referring now to Fig. 12, the motor 29 drives the rotor blades 22 insubstantially the same manner described above in connection with theother modifications. The pump and motor combination described in Fig. 11may be used in subform in that modification shown in Fig. 12. However,in Fig. 12, an auto- "matic by-pass valve 325, responsive to pressure inthe high pressure line motor 292 may prevent from the ump to theoverloading of the hydraulic system at excessive pitch settings of therotor blades 39, in case such condition obtains. For the purpose ofvarying the thrust in this modification, I employ a worm pitchadjustment 339 which may be of the kind disclosed in Patent No.2,318,259, entitled, Direct Lift Aircraft, filed April 6, 1940. Tocontrol the pitch of the blades 32, pedals 332 may be operated by thepilot. This type of control is applicable in that form of the inventiondisclosed in Fig. 10 for varying the pitch of the blades 96' manually incombination with the structure shown therein and may incorporate ahydraulic power boost, if desired, such as in that modification of theinvention shown in Fig. 11.

Several of the features of the different modifications shown anddescribed above can be employed with other parts of the systems ifdesired. For this reason, I wish not to be limited only to those formsshown and described, but by combination and subcombination thereof, asset forth in the following claims.

I claim:

1. In a rotary wing aircraft, a main-sustaining rotor, an auxiliaryanti-torque rotor, an engine, fixed ratio drive means for driving eachof said rotors at predetermined relativ speeds, said auxiliary rotorhaving means for varying its thrust to compensate for variations in thetorque of said main rotor, means for measuring main rotor torqueincluding a movable member, spring means for normally balancing thetorque exerted by said main rotor on said movable member, meansoperatively connecting said member with said thrust varying meansincluding rigid linkage elements, and pilot operated means having anoperative connection with said linkage elements for adjusting saidthrust varying means of said auxiliary rotor independently of theposition of said movable member. 2. In a rotary wing aircraft, a mainsustaining rotor, an auxiliary anti-torque rotor, an engine, fixed ratiodrive means for driving each of said rotors at predetermined relativespeeds, said auxiliary rotor having means for varying its thrust tocompensate for variations in the torque of said main rotor, means formeasuring main 'rotor torque including a movable member, spring meansfor normally balancing the torque exerted by said main rotor on saidmovable member, linkage means operatively connecting said member withsaid thrust varying means, and pilot operated means for adjusting saidthrust varying means independently of said torque measuring means havingan operative connection to said linkage means between said movablemember and said thrust varying means.

3. In a rotary wing aircraft, a main sustaining rotor, an auxiliaryanti-torque rotor, an engine, fixed ratio drive means for driving eachof said rotors at predetermined relative speeds, said auxiliary rotorhaving means for varying its thrust to compensate for variations in thetorque of said main rotor, means for measuring main rotor torqueincluding a movable member, spring means for normally balancing thetorque exerted by said main rotor on said movable member, linkage meansoperatively connecting said member with said thrust varying means, andpilot operated means for adjusting said thrust varying means relative tosaid balanced movable member including an operating member having anoperative connection with said linkage means between said thrust varyingmeans and said movable member and movable relative to said movablemember in any balanced position of the latter.

4. ,In a rotary wing aircraft, a main sustaining rotor, anauxiliaryanti-torque rotor, an engine for driving said rotors, saidauxiliary rotor having means for varying its thrust to compensate forvariations of torque of said main rotor, means for measuring main rotortorque including a movable member, spring means for normally balancingthe torque exerted by said main rotor on said member, actuating meansoperatively connecting said member and said thrust varying means andresponsive to changes in position of said member forradjusting'thethrust varying means of said auxiliary rotor including a toggle havingtwo pivotally connected links movable between an aligned position and anangularly related position, and pilot operated means having an operativeconnection to the common pivot of said links.

HARRY THOMAS JENSEN.

References Cited in the file of this patent UNITED STATES PATENTS

